The present invention relates to a commutator motor that is available to vacuum cleaners, electric power tools and so on, and particularly the commutator motor that can operate from either AC or DC power sources, and has excellent performance of preventing coils from being burnt at overload.
In recent years, the need for commutator motors that are used in electric appliances such as vacuum cleaners, electric power tools and so on, and can operate from either AC commercial power source or a DC power source such as battery, is increasing.
For example, Japanese Patent Early Publication [KOKAI] No. 6-335214 discloses a commutator motor with a two-layer structure of coil windings for low and high voltages that are wound in iron-core slots of a rotator. When the commutator motor is operated from a 12 V rechargeable battery, a switch makes a connection between the battery and a brush for low voltage, so that electric current is allowed to flow in order of batteryxe2x80x94brush for low voltagexe2x80x94commutator for low voltagexe2x80x94coil windings for low voltagexe2x80x94commutator for low voltagexe2x80x94brush for low voltagexe2x80x94battery. Thus, the commutator motor can be operated by use of the low voltage.
On the other hand, when the commutator motor is operated from 100 V AC power supply, the switch makes a connection between a brush for high voltage and the 100 V power source, so that electric current is allowed to flow in order of 100 V power sourcexe2x80x94full-wave rectificationxe2x80x94brush for high voltagexe2x80x94commutator for high voltagexe2x80x94coil windings for high voltage commutator for high voltagexe2x80x94brush for high voltagexe2x80x94full-wave rectificationxe2x80x94100 V power source. Thus, the commutator motor can be also operated by use of the high voltage.
By the way, in the commutator motor mentioned above, the coil windings for high voltage used in the connection with the 100 V AC power source are provided at the bottom side of the iron-core slots, and the coil windings for low voltage used in connection with the battery are provided at the top side of the iron-core slots, i.e., at the outside of the coil windings for high voltage. Due to this structure, when the commutator motor is operated by use of the 100 V AC power source, a cooling efficiency of the coil windings for high voltage provided at the bottom side of the iron-core slots becomes poor. Consequently, an increase in temperature of the coil windings easily occurs, and there is a fear that the coil wires are burnt at overload.
Therefore, a concern of the present invention is to provide a commutator motor, which can operate from either AC or DC power sources, shows an equal motor characteristic in both cases of using the AC and DC power sources, and has excellent performance of preventing coils from being burnt at overload.
That is, the commutator motor comprises an iron core having plural slots that are used for coil winding, a rotation shaft inserted in a center of the iron core, and a pair of first and second commutators mounted on the rotation shaft at opposite ends of the iron core. A first coil wire is connected to the first commutator, and wound on bottoms of the slots of the iron core to form an inner coil. A second coil wire is connected to the second commutator, and wound on the inner coil in the slots of the iron core to form an outer coil. In addition, the commutator motor is provided with a first terminal that can be connected to a first power source to supply electric power of the first power source to the first coil wire through the first commutator; and a second terminal that can be connected to a second power source to supply electric power of the second power source to the second coil wire through the second commutator. In the present invention, the commutator motor is characterized in that a diameter of the second coil wire is smaller than that of the first coil wire.
Since the outer coil formed by use of the second coil wire having the small diameter is disposed at the peripheral side of the iron core, it is possible to efficiently cool the second coil wire in order to prevent the second coil wire from being burnt at overload. In particular, when a cooling unit such as cooling fans for cooling the second coil wire is arranged around the outer coil, the cooling efficiency of the second coil wire can be facilitated to provide a further improvement of safety. Thus, in the present invention, it is possible to provide the commutator motor with a high degree of reliability in safety by preventing the second coil wire from being burnt.
In the commutator motor of the present invention, it is preferred that a winding start position of the second coil wire of the outer coil is displaced at 90 degrees about the iron core with respect to a winding end position of the first coil wire of the inner coil. In this case, it is effective to minimize the occurrence of waste space between the first and second coils formed by use of the coil wires having different diameters, and to downsize the commutator motor.
In addition, in the commutator motor described above, it is preferred that the first terminal is adapted for use in a DC power source for supplying a large current that works as the first power source, and the second terminal is adapted for use in an AC power source for supplying a small current that works as the second power source, and the inner and outer coils are formed such that a motor output provided by use of the first power source is substantially equivalent to the motor output provided by use of the second power source.
Further features and advantages of the present invention will be clearly understood from the best mode for carrying out the invention described below referring to the attached drawings.